For VOIP: SQM with/without VLANS, VLANS with/without SQM

A noob question, but I haven't found any information that spells this out:

1)For protecting VOIP call quality, what would VLANS accomplish without using SQM? As I understand, just simply separating a LAN into separate VLANS would reduce collisions/damaged packets.

  1. What effect would SQM on the WAN have without using VLANS? SQM seems to reduce latency/bufferbloat, which I believe would help with audio calls even without VLANS.

  2. Lastly, what is the effect of SQM with VLANS?

Trying to better understand the roles of the two, both together and independently, with regard to VOIP. Thank you.

VLANs allow you to isolate different traffic (those using different VLAN IDs, by default only traffic with the same VLAN ID is in the same L2 domain).
SQM is a combination of a traffic shaper and an AQM (advanced/active queue management)
These are really orthogonal things to each other that solve different issues.
For protection of VoIP you want both traffic isolation, but more some method to allow the relatively sparse VoIP traffic (typically in the range of ~100Kbps) to be not "suprresed" by more active traffic flows. That is something the FQ-scheduler in SQM's fq_codel od cake will essentially give you (as long as that VoIP flow stays below its equitable capacity share an FQ scheduler will not let it be crowed out by bigger flows).

Again orthogonal. Whether you need one or more VLANs on your WAN side really depends on your ISP, some require different VLAN IDs for voice and data, some use an identical VLAN ID and some do not use VLANs. SQM mostly does not care all that much, you just need to figure out where to instantiate SQM to cover all bases.

The same as with VLANs mostly :wink: SQM can help keeping the latency under saturating load acceptable, and help share the wan capacity fairly between all flows (it also offers fancier isolation/fairness modes, but fow-fairness is at its essence).

I hope I could help, if not just ask more questions, please.